1. Field of the Invention
The present invention relates to a vessel propulsion apparatus that propels a vessel and to a method for manufacturing the vessel propulsion apparatus.
2. Description of the Related Art
U.S. Pat. No. 8,616,929 discloses a vessel propulsion apparatus that includes an outboard motor. The outboard motor includes a drive shaft that is rotationally driven by an engine, a drive gear that is connected to the drive shaft, and a front gear and a rear gear both of which engage the drive gear. The outboard motor further includes a dog clutch that selectively engages either the front gear or the rear gear and a propeller shaft that rotates together with the dog clutch.
When the engine causes the drive shaft to rotate, the drive gear rotates, and, in response to its rotation, the front gear and the rear gear rotate in mutually opposite directions. The rotation of the front gear or that of the rear gear is transmitted to the propeller shaft through the dog clutch. As a result, the propeller rotates in a normal rotation direction or in a reverse rotation direction, and a thrust that propels a vessel forwardly or backwardly is generated.
A thrust in a forward direction that propels a vessel forwardly (hereinafter, referred to as “forward-direction thrust”) is transmitted to a hull through the front gear. The forward-direction thrust generated by the rotation of the propeller is entirely transmitted to the front gear. A thrust applied to a thrust bearing that supports the front gear increases as the output of the engine increases. Thus, the thrust bearing is required to have a large size to sustain the thrust. If the thrust bearing is enlarged, the torpedo diameter of a lower case that contains the thrust bearing and the gears would increase, and the resistance of water applied to the outboard motor during traveling would increase.